Hmmm very hard question cos I was never much of a Priest fan but then I saw them for the first time last year and they were jawdroppingly awesome live. I went mainly to see The Scorpions but Priest were absolutely immense. I've seen Maiden only the once and it was years ago but I am seeing them in December - so just to summarise what I'm rambling on about - I would say
Priest definitely for me but after I see Maiden in December I might well prefer Maiden!!!!
Absolutly no knock towards the Gods that are Iron Maiden, but Judas Priest holds a special place with me that makes me choose them.
Although, 'Seventh Son...' is one of the greatest records EVAR!
I love them both, but as a teenager in the 80s it was definitely Maiden. These days I find that classic Priest has more of an appeal to me than classic Maiden. Turning to their recent stuff, 'Angel of Retribution' was great, but I'd rather listen to 'Dance of Death' or 'Brave New World'. So it's a tie!